Integrated window, antenna, and waveguide with plasma alleviation

ABSTRACT

A method and an apparatus for cooling an electromagnetic wave permeable antenna window, and for alleviating a boundary layer of dense plasma, particularly for use in high performance reentry space vehicles having a sharp or conical configuration. The window, in a shock mounting, is of multilayered construction, having alternating shock absorbent bonded layers with channels or apertures spaced throughout. Gas, such as silicon tetrafluoride or sulfur hexafluoride, flows through an associated waveguide and is introduced, through the channels or apertures, into and through the window. As the coolant gas passes through the window, the window is cooled and does not ablate. Shear forces are used to maintain the window/ablator mold line. The gas then flows into the boundary layer of dense plasma, reducing the electron concentration of the plasma, and increasing the capability of transmitting or receiving electromagnetic waves.

United States Patent 1191 1111 3,846,798

Carl Nov. 5, 1974 INTEGRATED WINDOW, ANTENNA, AND

WAVEGUIDE WITH PLASMA Primary ExaminerMaynard R. Wilbur ALLEVIATIONAssistant Examiner-Richard E. Berger [75] Inventor: James R. Carl,Bridgeton, Mo. gi z gq f iz or firm-Harry Herbert [73] Assignee: TheUnited States of America as v represented'by the Secretary of the 57ABSTRACT United States Air Force, Washington DC A method and anapparatus for cool ng an electromagnenc wave permeable antenna wmdow,and for [22] Filed: Aug. 12, 1968 alleviating a boundary layer of denseplasma, particularly for use in high performance reentry space vehi-[21] Appl' 752082 cles having a sharp or conical configuration. Thewindow, in a shock mounting, is of multilayered construc- [52] U.S. Cl.L 343/705, 343/784, 343/872, tion, having alternating shock absorbentbonded layers 333/98 R, 3925/65 with channels or apertures spacedthroughout. Gas, [5 1] Int. Cl. H0lq 1/28 such as silicon tetrafluorideor sulfur hexafluoride, [58] Ifield of Search 343/784, 783, 705; flowsthrough an associated waveguide and is intro- 333/22 F, 98, 98 P;313/35; 325/65 duced, through the channels or apertures, into andthrough the window. As the coolant gas passes [56] References Citedthrough the window, the window is cooled and does UN STATES PATENTS notablate. Shear forces are used to maintain the win- 2577 463 12/1951l-lansellm 343/784 dOw/ablato mold line' The gas thenflows into the2:947:956 8/1960 Alexander et al. 333/98 boundary f w dense Plasma, gthe electron 3,110,000 11/1963 Churchill 333/98 P ux cohcehtrahon 0f thePlasma, and mcreasmg the p 3,128,965 4/1964 Ziemer 325/65 ux bility oftransmitting or receiving electromagnetic 3,277,375 10/1966 Nelson et al325/65 waves.

315331223 5/1323 7 ib bifi'. 537/3; 10 cla-ms, s

INTEGRATED WINDOW, ANTENNA, AND WAVEGUIDE WITH PLASMA ALLEVIATIONBACKGROUND OF THE INVENTION This invention relates to a method and anapparatus for cooling an electromagnetic wave permeable antenna window,and, additionally, for alleviating a boundary layer of dense plasma.

This invention is particularly well suited for use, generally, in highthermal and high shear environments and, more specifically, in highperformance reentry space vehicles having a sharp or conicalconfiguration.

Electromagnetic wave permeable windows are not new. They have been madeof glass, mica and, more recently, of alumina ceramic. They have beenvacuum sealed or otherwise affixed to antennas, such as the horn type,and to output waveguides. Their use has been extended, in fact, tocooling structures, but as far as is known, without great success.Cooling, for example, by air, water and even specific gases, has beenattempted at or contiguous to the periphery of the window. The resultshave been uneven cooling of the window, particularly at the centerthereof, and resultant cracking of the window. Even where cracking didnot occur, the structure of the window or of the coolant carrier, orboth, resulted in significant loss of transmission of electromagneticwaves from theantenna or output waveguide.

In addition, in connection with the use of electromagnetic permeablewindows in antenna or output waveguides for use in airborne vehicles,particularly sharp or conical configurated high performance reentryvehicles, there is the problem of dense plasma which can prevent, or atleast severly limit, propagation or transmission of electromagneticwaves to or from the vehicle. This transmission limitation is well-knownnot only to those skilled in the art, but also to the general public andto commercial communications mass media, such as television, which oftenrefers to this phenomena, in connection with coverage of space flights,as communications interference or communications blackout caused by aplasma layer or a plasma sheath.

My invention cools electromagnetic wave permeable windows withoutdeleterious effect and, concurrently, eliminates or at least minimizesthe problem of transmission limitation caused by the dense plasma in,near, or about the window, when the window is used in an airbornevehicle.

SUMMARY OF THE INVENTION My invention pertains to a method and anapparatus for cooling an electromagnetic wave permeable antenna windowand for alleviating a boundary layer of dense plasma. More particularly,this invention relates to an integrated electromagnetic wave permeablewindow, antenna, and waveguide, with plasma alleviation, for use, forexample, in high performance reentry space vehicles having a sharp orconical configuration.

Thus, an object of my invention is to provide a novel electromagneticwave permeable window for use with an antenna or a waveguide.

Another object of my invention is to provide an electromagnetic wavewindow which can be simply and economically constructed and which can beefficiently cooled without any deleterious effect.

Still another object of my invention is to provide an electromagneticwave permeable window which can be used in high thermal and high shearenvironments.

A further objectof my invention is to provide an electromagnetic wavepermeable window for use in high performance reentry space vehicleshaving a sharp or conical configuration.

A still further object of my invention is to provide a novel method ofcooling an electromagnetic wave permeable wave window.

An additional object of my invention is to provide a method foralleviating a boundary layer of dense plasma in, near and about anelectromagnetic wavepermeable window to eliminate, or at least uminimze,the problem of transmission limitation caused by said dense plasma.

These, and still other, objects of my invention will be-- come readilyapparent after a consideration of the description of my invention andreference to the drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view, in schematicform, ofa portion of a sharply configurated reentry space vehicleshowing an embodiment of my invention;

FIG. 2 is a cross-sectional view, in schematic form, taken along lineI-I of FIG. 1;

FIG. 3 is also a cross-sectional view, in schematic form, buttaken alongline IIII of FIG. 1;

FIG. 4 is a top plan view, in schematic form, of a portion of a sharplyconfigurated reentry space vehicle showing another embodiment of myinvention; and

FIG. 5 is a cross-sectional view, in schematic form, taken along lineIII-Ill of FIG. 4.

DESCRIPTION OF THE EMBODIMENTS With reference to FIG. 1, wherein aportion of a sharply configurated reentry space vehicle 10 is shown, theelectromagnetic wave permeable window 21 is flush, or essentially levelwith, the ablative surface or shield 11 of space vehicle portion 10.Window 21 is a part of an integrated window-antenna-waveguide assembly20, of which the antenna and waveguide component parts are not shown inFIG. I.

In FIG. 2, the ablative surface or shield 11, the window 21, and theantenna-waveguide portion of the integrated window-antenna-waveguideassembly 20, and their relative positioning are better seen. The window21 is at the antenna (or output waveguide) interface 24 and said windowis of the multilayered type, i.e., layered construction, withalternating bonded layers, such as 22 and 23, preferably of fused silicalayers with less dense layers which are sintered until bonds are formed.

seen. It is to be noted that the alternating bonded layers 22 and 23 ofwindow 21 are also contoured.

Window 21 is in a suitable shock mounting (not shown).

In FIGS. 4 and 5 are depicted views of another embodiment of myinvention.

In this embodiment, and specifically with reference to FIG. 4, there isa coolant fluid outlet 55 disposed adjacent to the electromagnetic wavepermeable window 51, of integrated antenna-window-waveguide assembly 50,in ablative surface or shield 41 of space vehicle portion 40.

In FIG. 5 is shown window 51 with alternating bonded layers such as 52and 53, preferably of fused silica layers with less dense layers whichare sintered until bonds are formed, antenna 54, and coolant fluid flowconduit 55, just upstream of window 51, as they are relativelypositioned in ablative shield 41.

It is to be noted that in this embodiment, window 51 does not have anyartificially constructed channels, such as 25, FIGS. 2 and 3.

The coolant fluid, such as silicon tetrafluoride gas or sulfurhexafluoride gas 56, flows through conduit 55.

Window 51 and coolant fluid flow conduit 55 are flush with thecontouring of ablative shield 41 at the air flow boundary surface 57.

Window 51 is in a suitable shock mounting (not shown).

MODE OF OPERATION OF THE PREFERRED EMBODIMENT As to the embodiment shownin FIGS. 1, 2 and 3, the gas coolant 28, such as silicon tetrafluorideor sulfur hexafluoride, is introduced through conduit 26 which in thiscase serves the dual purpose of coolant delivery system and waveguide.The flow of the gas coolant through the waveguide, as such, protects thewaveguide from high voltage breakdown.

Coolant gas 28 leaks into electromagnetic wave permeable window 21through artifically constructed channels 25, cooling the window. As aresult, window 21 does not ablate. Shear forces are used to maintain thewindow/ablator mold line or air flow boundary 27, so that if theshearing forces are sufficiently strong, window 21 will shear at thebond lines between alternating bonded layers, such as 22 and 23, as aparticular bond line is reached and is acted upon by the shearingforces. It is here to be noted that the multilayered construction ofwindow 21 with shock absorbent bonding layers, such as 22 and 23,preferably of fused silica layers with less dense layers which aresintered until bonds are formed, together with the shock mounting (notshown) of window 21, permits window 21 to withstand much higher shocklevels than any known conventional solid electromagnetic wave permeablewindow. The layered construction, with alternating bonding layers, ofwindow 21 serves as acoustical mismatch for the attenuation of shockwaves.

Coolant gas 28, after flowing through artifically constructed channels25, passes into boundary layer 27, a region of high temperature and highelectron concentration, cools that boundary layer 27 and, thereby,reduces the electron concentration, or dense plasma, and eliminates, orat least minimizes, the problem of transmission limitation caused by thedense plasma.

As to the embodiment shown in FIGS. 4 and 5, the

6 coolant gas 56, such as silicon tetrafluoride or sulfur hexafluoride,is introduced through conduit 55 into boundary layer 57, which is aregion of high temperature and high electron concentration. There, thecoolant gas 56, moving downstream, cools window 51 by cooling boundarylayer 57. Additionally, and as a result of cooling of boundary layer 57,the electron concentration or dense plasma is eliminated, or at leastminimized, so that transmission of electromagnetic waves issignificantly improved.

Window 51 is structured similarly to window 21, FIGS. 2 and 3, except ofcourse that it does not have artificially constructed channels 25, FIGS.2 and 3. In

essence, it does not ablate; shear forces are used to maintain thewindow/ablator mold line or air flow boundary 57; window 51 will shearat the particular or appropriate bond line if sufficient shearing forceis applied; and, window 51 will withstand much higher shock levels thanconventional solid electromagnetic wave permeable windows because, inaddition to the foregoing, it is also shock mounted (not shown) and itslayered construction, with alternating bonding layers, serves asacoustical mismatch for the attenuation of shock waves.

While there has been shown and described the fundamental novel featuresof my invention, as applied to the preferred embodiments, it is to beunderstood that various substitutions and omissions may be made by thoseskilled in the art, without departing from the spirit of the invention.For example, the window may be used as waveguide window, rather than anantenna window; the configuration or periphery of the window may becircular, or otherwise configurated as necessary or desired; theartifically constructed coolant flow channels through the window may bereplaced by natural channels, simply by using gas-perviouselectromagnetic wave permeable materials as the bonded layers; thewindow laminates may be flat, rather than contoured; and the windowlaminates may be of pyrolytic boron nitride layers with hot pressedboron nitride as bonding layers.

What I claim is:

1. An electromagnetic wave transmitting and receiving structure,comprising:

a. an antenna;

b. an electromagnetic wave permeable window which includes:

(1). a plurality of alternating bonded layers; and

(2). a plurality of hollow channels, essentially parallel to each otherand extending throughout said window.

c. means for supporting said electromagnetic wave permeable windowwithin said antenna; and

d. a waveguide affixed to said antenna.

2. The apparatus, as set forth in claim 1, wherein said alternatingbonded layers are of fused silica and of less dense silica which hasbeen sintered.

3. The apparatus, as set forth inclaim 1, wherein said alternatingbonded layers are of pyrolytic boron nitride and of hot pressed boronnitride.

4. An apparatus for cooling an electromagnetic wave transmitting andreceiving structure, and for alleviating a boundary layer of denseplasma, in a high performance reentry space vehicle, comprising:

a. an antenna;

b. an electromagnetic wave permeable window, having a plurality ofalternating bonded layers of fused silica and of less dense silica whichhas been sintered, and having a plurality of hollow channels essentiallyparallel to each other and extending throughout said window;

c. means for supporting said electromagnetic wave permeable windowwithin said antenna;

(1. a waveguide affixed to said antenna;

e. a coolant fluid; and

f. means for conducting said coolant fluid to said hollow channels ofsaid electromagnetic wave permeable window.

5. The apparatus, as set forth in claim 4, wherein the coolant fluid issilicon tetrafluoride.

6. The apparatus, as set forth in claim 4, wherein the coolant fluid issulfur hexafluoride.

7. The apparatus, as set forth in claim 4, wherein the means forconducting said coolant fluid to said hollow channels of saidelectromagnetic wave permeable window is the said waveguide.

8. An apparatus for cooling an electromagnetic wave transmitting andreceiving structure, and for alleviating a boundary layer of denseplasma, in a high perform- I ance reentry space vehicle, comprising:

a. an antenna;

10. The method of cooling an electromagnetic wave transmitting andreceiving structure, and of alleviating a boundary layer of denseplasma, in a reentry space vehicle having an electromagnetic wavepermeable window, comprising the step of flowing a coolant fluid throughhollow channels in said window.

1. An electromagnetic wave transmitting and receiving structure,comprising: a. an antenna; b. an electromagnetic wave permeable windowwhich includes: (1). a plurality of alternating bonded layers; and (2).a plurality of hollow channels, essentially parallel to each other andextending throughout said window. c. means for supporting saidelectromagnetic wave permeable window within said antenna; and d. awaveguide affixed to said antenna.
 2. The apparatus, as set forth inclaim 1, wherein said alternating bonded layers are of fused silica andof less dense silica which has been sintered.
 3. The apparatus, as setforth in claim 1, wherein said alternating bonded layers are ofpyrolytic boron nitride and of hot pressed boron nitride.
 4. Anapparatus for cooling an electromagnetic wave transmitting and receivingstructure, and for alleviating a boundary layer of dense plasma, in ahigh performance reentry space vehicle, comprising: a. an antenna; b. anelectromagnetic wave permeable window, having a plurality of alternatingbonded layers of fused silica and of less dense silica which has beensintered, and having a plurality of hollow channels essentially parallelto each other and extending throughout said window; c. means forsupporting said electromagnetic wave permeable window within saidantenna; d. a waveguide affixed to said antenna; e. a coolant fluid; andf. means for conducting said coolant fluid to said hollow channels ofsaid electromagnetic wave permeable window.
 5. The apparatus, as setforth in claim 4, wherein the coolant fluid is silicon tetrafluoride. 6.The apparatus, as set forth in claim 4, wherein the coolant fluid issulfur hexafluoride.
 7. The apparatus, as set forth in claim 4, whereinthe means for conducting said coolant fluid to said hollow channels ofsaid electromagnetic wave permeable window is the said waveguide.
 8. Anapparatus for cooling an electromagnetic wave transmitting and receivingstructure, and for alleviating a boundary layer of dense plasma, in ahigh performance reentry space vehicle, comprising: a. an antenna; b. anelectromagnetic wave permeable window, having a plurality of alternatingbonded layers of fused silica and of less dense silica which has beensintered; c. means for supporting said electromagnetic wave permeablewindow within said antenna; d. a waveguide affixed to said antenna; e. acoolant fluid; and f. means for conducting said coolant fluid to theboundary layer.
 9. The apparatus, as set forth in claim 8, wherein themeans for conducting said coolant fluid to the boundary layer is aconduit upstream of said electromagnetic wave permeable window.
 10. Themethod of cooling an electromagnetic wave transmitting and receivingstructure, and of alleviating a boundarY layer of dense plasma, in areentry space vehicle having an electromagnetic wave permeable window,comprising the step of flowing a coolant fluid through hollow channelsin said window.